As for the second part I have to disagree. The Nords use to practice magic but for one reason or another it fell into disfavor. Same with Redguards, though with them I think we have a good reason as to why they turned from it. Both groups turned from it for cultural reasons.
I just want to stress the point that culture plays a large part here. If Certain "Races" were predisposed to fight a certain way then wouldn't all mer favor magic since that's what their ancestors fought with? When looking at the lore we see that is clearly not the case.
Sure, culture, family, and life experience all play a role. But that doesn't mean a Redguard's love of adventure and fighting is "all cultural stuff" as you said earlier. It may very well be partially inherited.
Your magic argument seems kinda nonsensical to me.